Design and Assessment of an AC-SDBD Plasma Reactor for Acceleration of the Deflagration to Detonation Transition in a Dimethyl Ether Electrofuel

Abstract

Recent developments in detonation engines hold immense promise for the enhanced sustainability and performance of both air-breathing propulsion and rockets. The imminent next step in achieving operationally viable detonation engines lies in improving the control and efficiency of the propagating detonation waves that provide high specific impulse. This can be achieved through manipulating the speed of the deflagration to detonation transition (DDT) in a reacting flow. Treating a fuel/oxidizer premixture with low-temperature plasma represents an attractively simple and effective option for accelerating DDT through enhancing ignition-shock interaction and accelerating reaction kinetics with the production of active species to promote ignition. However, only nanosecond volumetric dielectric barrier discharge (VDBD) plasma configuration have been previously verified for this purpose. VDBD plasmas experience limitations in applicable combustion channel sizes and pressures, and a nanosecond discharge profile cannot leverage plasma electric field momentum transfer in reactants. Therefore, the widespread practical implementation of plasma DDT acceleration technologies necessitates a more versatile DBD plasma reactor configuration and discharge design. Furthermore, environmental concerns surrounding combustion engines require the study and characterization of new, sustainable fuel alternatives.

This thesis responds to these exigencies through the development of an alternating current surface dielectric barrier discharge (AC-SDBD) plasma for the purpose of accelerating DDT in a microchannel containing a DME/O2/Ar premixture. In addition to its flexible applicability to combustion channels of varying sizes and pressures, the AC-SDBD plasma reactor's potential merits arise from its ability to generate a highly ionized plasma capable of leveraging shock-boundary interactions and ionic winds to enhance autoignition. The objectives of this thesis are twofold: (1) to design and characterize an AC-SDBD plasma reactor (2) to test the performance of this reactor in accelerating DDT in the combustion of a sustainable e-fuel, dimethyl ether (DME), using chemiluminescence imaging. While substantial progress is made in the development and evaluation of the reactor, structural effects caused by electrode geometry in the channel ultimately dominate in terms of producing autoignition and detonation, such that the effect of the plasma itself on DDT in the DME/O2/Ar mixture cannot be characterized in isolation. However, continued improvements in design robustness could allow for characterization of the AC-SDBD plasma's effects on DDT. To conclude this thesis, a concept design and literature review is presented regarding the implications of AC-SDBD plasma-assisted e-fuel detonation propulsion for robotic space exploration, particularly astrobiologically motivated science missions.